Some old data from 2009 that I finally got round to dusting off. Turns out that blood group A has more consistent elevated breath hydrogen (after administration of lactulose) than the other blood types (A non-secretors being highest). High breath hydrogen after lactulose administration is a sign of malabsorption/ small intestinal bacterial overgrowth. Culling those with the highest baseline readings and simply giving each a copy of my book 'Eat Right For Your Type' and having them follow the recommendations for their blood type for three weeks resulted in an significant overall decrease in the breath hydrogen readings.